Trunking system



1 .1 632 901 June 21, 927 H- B. JOHNSON TRUNKING sys'rnm Filed Oct. 30.1925 2 Sheets-Sheet 1 H. B. JOHNSON wauuxme SYSTEM Filed 001:. 30. 19252 Sheets-Sheet 2 June 21', 1927. I 1,632,901

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Patented p June 21, 1927.

UNITED sTATss PATENT. oFFIcE,

HERBERT B. JOHNSON, OF BROOKLYN, NEW YORK, ASSIGNOR TO BELL TELEPHONE TLABORATORIES, INGORPORAYIED, 033 NEW YORK, N. Y., A CORPORATION OF NEWYORK.

TRUNKING SYSTEM.

Application filed October 30, 1925. Serial N0. 65,744.

This invention relates to telephone systems and more particularly tosystems for trunking between a plurality of subscribers office's,sub-stations and main stations.

Systems of this type generally provide for means whereby a plurality ofoffices located in a group or a certain zone a considerable distanceaway from a main office are arranged with comparatively short trunklines leading from these zone offices to a centrally located junctionpoint or office from which a number of comparatively longer trunk linesare provided to the main office. In the type of systems to which theimprovements in accordance with this invention relate, the number oftrunks between the junction office and the main office are equal to thenumber of trunks from each of the zone offices to the junction office.

It is an object of this invention to reduce the cost of trunking betweenoffices and cheapen and simplify the operation of systems of thisgeneral class. and particularly to the type in which the common trunksoutgoing to a main office are normally connected at the junction officeto all of the branch trunks incoming thereto from the zone: offices.

To attain this and other objects of the invention there is provided inaccordance with one feature thereof means whereby if a trunk outgoingfrom a zone office is taken for use. all the trunks out-going from theother zone offices normally connected to the same common trunk outgoingfrom the junction office are disconnected from this common trunk leavingthe connection from the zone office from which the connection was madeintact. Another feature of the invention resides in the provision ofmeans whereby a busy condition is established for all of saiddisconncctec trunks. Another feature of the invention resides in theprovision of means whereby in an arrangement of this sort, group busyconditions are estahlished for all of the trunks outgoing from the zoneoffices when all of the main trunks outgoing from the junction officeare in use.

It should be understood that this invention is not limited to thespecific arrangement mentioned. above 111 which trunks from a pluralityof zone offices are connected at a junction office to a common trunkextended to a main office but that such zone trunks may very well extendto and terminate at different operators switchboards in the same officeor to anyarrangement of a similar nature where a plurality of branchtrunks connected to a common trunk regardless of where these branchtrunks begin and where the common trunk terminates.

In the attached drawings, Fig. 1 illus trates an arrangement inaccordance with this invention in which a single common trunk outgoingfrom a junction office is shown with a. plurality of zone trunks normally connected thereto and terminating in a plurality of zone officesand a portion of an ordinary cord circuit at one of said zone officeswhereby a zone trunk terminating thereat may be seized, whileFig. 2shows a.

modified form of the invention with an idle or busy trunk indentifyingarrangement applied thereto this circult arrangement being the subjectmatter of a copending appli-.

cation of L. L. Eagon, Serial No. 65,876,

filed on even date with the filing of this application. v Referring nowto Fig. 1 there IS shown the detail equipment for zone trunks l, 2 and 3outgoing respectively from zone offices A, B and C and the circuitarrangement at a junction office D whereby said zone trunks areconnected together to a common trunk 4 leading to a main office. Itshould be understood that a plurality of trunks such as 4i may besimilarly arranged and equipped at the junction office and thatacorresponding number of zone trunks may be provided from the variouszone offices.

To make clear the operation of this sysdecides .to extend a connectionto the comtern a connection from the zone office A lighting of lamp andthe operation of relay 11.

Relay 11 in operating opens at its innerarmature and back contact abridge circuit normally closed across the tip and ring conductors ofzone trunk 1. Another circuit closed by the insertion of plug 6 intojack 7 causes the operation of relay 13 at junction oifice D. Thiscircuit is as follows: battery, lower right-hand winding of repeatingcoil 15 of the cord circuit at E, supervisory relay 16, ring contacts ofplug 6 and jack 7, lower winding of relay 13, contacts 17 of relay 18,upper winding of relay 13, tip contacts of jack 7 and plug 6,

armature and frontcontact of relay 9, upper right-hand winding ofrepeating coil 15 to ground. It should be noted that the circuit fortheoperation of relay 13 (lOGSDOt cause the operation of relays 13 and 1.3,although theyare connected in circuits to the common conductors 21 and22 as follows:

from the ring conductor of zone trunk 1, I

common conductor 21'andin parallel to the lower outer arinatures andback contacts oi relays 18' and 18", lower windings of relays "13' and13 u er inner armature and back contacts of relays 18 and 18, commonconductor 22, upper inner armature and back contact of relay'18, contact17, upper Wind'- ing of relay13 to the tip conductor of zone trunk 1 andalso parallel circuits from the common conductor 21, through tip andring conductors of zone trunks 2 and 3 and the windings of the bridgedrelays 12 and 12" to the upper windings of relays 13 and 18 to thecommon conductor 22. As shown by these circuits, tliewindings of relays13 and 13 are connected so that current in the two windings of theserelays oppose each other while the current through the windings ofrelays 13 are in series a ding relation.

Hence, relay 18 will operate and relays 13 and 13 will not be operatedon theseizure of zone trunk 1. It is to be understood that theelectrical characteristics of relays 12' and 12 may be such as not tooperate in the above c1rcuits on the seizure of zone trunk 1. Relay 13in operating closes atits arma 'ture and front contact a connection toground for the operation of relays-18 and 18", in the circuits for zonetrunks 2 and 3 and for other similar relays of the circuits for otherzone trunks that may be norn ally connected to the common trunk 4t andextend to other zone offices. The circuits for these relays maybe tracedas follows: frornbattery through the windings of relays 18" and 18andover the armatures and back contacts of relays l3 and 13 in parallelto ground at the armature and front contact of relay 13. ,Relays 18 and18" operate in these circuits and disconnect respectively the zonetrunks 2 and 3 at their upper outer and lower outer armatures and backcontacts from the common leads 20 and 21, to which all of the zonetrunksfrom the various zone oflices are normally connected. It should be notedthat relay 18 is not op erated in this circuit as the connection frombattery through its winding is opened on the o iieration of relay 13 sothat the conductors of zone trunk 1 are maintained connected to thecommon leads 20 and 21 which are in fact the tip andring conductors oftrunk 1- leading to the main ofliee. The operation of relays 18 and 18"closes circuits for the ()l'JQL'dlilOn of relays 12 and'12",respectively. The circuit for the operation of one of these relays willbe traced: battery,

lower non-inductive Winding of relay 18',

lower outer armature and front contact of relay 18, ring conductor ofzone trunk 2, winding of relay 12'. inner upper armature and backcontact of relay 11, tip conductor of zone trunk 2, upper outer armatureand front contact of relay 18, upper non-iuduc-' tive winding of relay1.8 to ground. 2 Re lays12 and 12 in operating close at "their Bowerarinzitures and front contacts circuits to battery for the sleeveterminals of the corresponding jacks 7 and 7". The circuit for sleeveterminal of jack 7' will be traced a battery, lower winding of relay11", lower armature and frontcontact of relay 12',

upper winding of relay 11, sleeve terminal of jack 7. These connectionsto battery for the sleeve terminals of jacks 7 and 7 "*thus provide busyconditions for these jacks so that in case an operator at any of theseoffices flllGIl'lDtS to make connection with the corresponding jackfshewill receive a busy indication as she touches the tip of a plug to the seeve of the pick as is well known in the art. The connection from theoperator at E from zone trunk 1 tothel main trunk 4. is now completedvthrough'the t p and ring I onductors.

As the connections beyondform no part of this invention, no furtherdescr ption of the extension of the connection will be made, except tosay that when the called subscriber at the opposite endof main trunk 4answers, a circuit will be completed for the operation of relay 25 asfollows: battery, lower inner armatures and front contacts of relays 18and 18". common, conductor 26,

lower winding of relay 25, ring conductor of trunk l, subscribers loop,back to the tip conductor of main trunk 4, upper windingof relay toground. The operation of relay 25 closes a shunt circuit through theretardation col 27 for the lower high re- ;sistance winding 'of relay 13as follows:

[areavailable;

ring conductor of zone trunltl, retardation coil 27, armature and;f'ront contact of relay 2'5, upperinnerarmaturev andback contact ofrelay 18, contacts17, upper winding of relay 13 to the tip conductor ofzone This circuit across the high re sistance winding of" relay" 13'decreases the resistance of the pathacross the; tip and ring conductorof zone trunk 1, causing the re- 1'ay'16 in the cordcircuit at'E tooperate and shunt the circuit for' supervisory lamp 1O whicli1now' isextinguished as an indication to the operator: at E, that the calledsubscriber has answered; a procedure which is well known in the art;

It'is'evident" that if" an operator in the zone office BF had rnadea-connection to zone trunk 2', the operations would have been thesame asdescribed above forthe call over trunk 1 from; zone ofiice A. In thiscase,,of course, relays l l" and- 13 at zone office B, relays 18ancl 18at the junction ofli'ce and. relays 12 and" 12" at the zone offices andC would have operated, so that a busy condition would have beenestablishcd for" the" jacks Tand 7 at the zone oih'ces" A and C'and';the zone trunks 1' and 3" would have been disconnected from the commonleads'20 and 21 while zone trunk 2' would have remained connectedthrough to the'con'rm'on trunk 4.

The so-called 'group busy testing arrangement's at the zone oflicesarearranged so that when all of'the main trunks outgoing from" thejunction ofli'ce areengaged an operator at any zone ofiice attemptingtoestahlish a connection over a zone trunk receives" the tone; Inperforming the standard well known trunk group busy test, thisarrangement is such that if' the operator at a zone office tries toestabl sh a connection over" a zone. trunk, she will test the jack of a;particular trunk to determine if any'comniontrunksat the junction officeIf no tone is received on testing this jack, sherwi ll-know that atleast i one trunlr is available" at the junction office andintesting'this particular jack-she will naturally also determine if thecorrespondmg common trunk 13 engaged: If this particularcommon" trunkIS'IIOt available she will test the. jacks of other trunks in the groupuntil an idle trunk'is found;

The circuit connections fortransmitting atrunk group busy t'oneto thejack of a designated. trunk in each zone office is arranged as follows:If it is considered that 210k 7 in, the zone office A is to be tested ortrunli group busy tone, it will. be seen that the-relays 11 and.12 areprovidedwith armatures and contacts so that whichever of these relays isoperated, a connection will be. established fronrthe sleeve of jack 7 toa common lead 50; Similar arniatures are provided for corresponding relas such as ll and 12 associated with avzone trunk 1 and for other zonetrunks ou-tgoi n-gfrom zone officer l. A'connection from lead 50 tothese contacts is in the nature of'a socalled chain connection, that is,if either ofjack 7 to the tone device51 will be completed and a tonewill be heard in the operatoi"s telephone set throughthe usual busy lead52 in the cord circuit.

Arrangements identical to this group trunk busy circuit of zone office Aare provided for the other zone offices Band C so that the operator inany of thesezone offices will" receive a busy toneywhe n all of thecommon trunks outgoing from junctionoflice'are engaged.

The modified form. er? the invention shown in Fig, 2 illustrates how adifferent idle or busy identifying arrangement may he applied to thetrunking system of this invention. This identifying arrange ment initself. forms no part of this invention but is disclosed and clai'med inthe*copending application of Lloyd L. Eagon, Serial No. 65,876, filed.on even date with the filing of'this application; This figure shows theterminal arrangement" of two trunks outgoing froma zone oflice-and'illustrates an arrangement whereby a signalassociated with one trunk isnormally lighted and the corresponding signals o'f the other trunks arenormally extinguished and whereby the signal of a precedingtrunk isextinguished and the signal of a succeeding trunk lighted in response tothe seizure of the preceding trunk.

The arrangement shown in this figure is practically the same as thatshown in Fig. 1 as far as the making-busy features are concerned exceptin the arrangement whereby the ring conductor is normally opened andarranged'to be closed when the relay 111 is operated and in thearrangement whereby relay 111 is operated from a separate sleeve relay100,. otherwise the functions of relays 111. and 112 are identicalwitlithe functions of relays 11 and 12, It will be notedthat inv thisarrangen'ient, as well as in the arrangement. shown in Fig. 1, eitherthe relay 111 or 1121s operated when the correspondmg-trunk becomesbusy, that 1s, relay 111 is operated when jack 10? becomesbusy by,

ill

being seized and relay 112 is operated when the corresponding jack atanother zone ofiice' is seized to make jack 107 busy A circuit isnormally closed for the signal 101 froinbattery, lower armature and backby the operation of either relay 111 or 112,

the circuit for signal 101 Will be opened at the lower armature and backcontact of either relay 111 or 112 and a circuit closed from batterythrough the lower armature and back contact of relay 112 through thelower armature and front contact of relay 111, or, from battery throughthe lower armature and front contact of relay 112 to a lead 150 of achain circuit that extends from the circuits of the trunk 1 to thecircuits of trunk 2 through the lower armatures and back contacts ofrelays 111 and 112 through the signal 101" to ground. Signal 101 nowbecomes lightedto indicate to the operator that trunk 2 is idle. Iftrunk 2 becomes busy by the operation of either of the relays 111 or112*, the lamp 101 Will be extinguished and the circuit will then beextended to the lead 150 to the next succeeding trunk at this ofiice. ItWill be seen, therefore, that only one lamp associated with one of thetrunks in this zone oflice will be lighted at the time to indicate thatthe corresponding trunk is idle. In this manner it Will be ordinarilyunnecessary for the operators at the zone offices to perform the usualbusy test on the jacks of the outgoing trunks. All that the operator hasto do is to observe Where a lamp is lighted and choose the correspondingtrunk for the next outgoing connection.

WVhat is claimed is: V j

1. In a telephone system, a junction ofiice, a'common trunk comprisingtip and ring conductor outgoing therefrom, a plurality of branch trunkseach comprising tip, ring and sleeve conductors incoming thereto andnormally having their tip and ring conductors connected in multiple tosaid common trunk, and means responsive to the seizing of any one of.said branch trunks for disconnecting the tip and ring conductors of allof said branch trunks from the tip and ring conductors of the commontrunk except those of the seized branch trunk and for establishing abusy condition on the sleeve conductor of said disconnected branchtrunks.

' 2. In a telephone system, a junction oflice, a common trunk comprisingtip and ring conductors outgoing therefrom, a plurality of zone offices,a branch trunk comprising tip, ring and sleeve conductors and having itstip and ring conductorsoutgoing from each zone oflice and terminating insaid j unction oflice, the tip andring conductors of said branch trunksbeing normallyconnected in multiple to the'tip and ring conductorsofsaid common trunk at said junction oflice, and means at said junctionoflice responsive to the seizurefof any one of said branch trunks fordisconnecting the and ring conductors of allof said branch trunks fromthe tip andring conductors of the common trunk except the. tip andring'eonductors of the seized branch trunk, and means operating over thetip and ring conductors of said disconnected branch trunks in responseto the seizure of the one branch trunk for establishing at the zoneofiices Where said disconnected branch trunksterminate a busy conditionon the sleeve terminals of said disconnected branch trunks.

3; In a telephone system, a junction oflice, a plurality of commontrunks. outgoing therefrom, a plurality of zone ofiices, a group oi:branch trunks incoming tothe unction ofiice from each zone ofiice eachcommon common trunk from allof the branch trunks to which it is.multipled exceptthe branch 7 trunk seized, and means responsive to theengagement of allof the'common trunks for establishing at each zoneofiice a busycondition indicating that all of the. trunks are engaged. H

common 4:. In a telephone system, aijunction oflice,

a plurality of common trunks outgoing therefrom, a plurality of zoneoffices, a group of branchtrunks incoming to the junction office fromeach zone ofiice, each common trunk belng normally connected; inmultiple to a branch .trunk incom ng from each zone office, means atsaid junction ofiice responsive to the seizureof any one of said branchtrunks for disconnecting thecorresponding to which it is multipledexcept the branch trunk seized, means responsive tothe enjunctionoffice,

a plurality of common trunks outgoing therefrom, a plurality of zoneoflices, a group of branch trunks incoming to the junction oflice fromeach zone ofiice, each common trunk being normally connected in multipleto a branch trunk incoming from each zone ofiice, means at'sa-idjunction ofiice responsive to theseizure of any on'eof said branchtrunks for disconnecting the corresponding common trunk from all of thebranch trunks common trunk from all of the branch trunks to which it ismultipled except the branch trunk seized, means for establishing a busycondition at the terminals of all disconnected branch trunks at thecorresponding zone ofiices responsive to the means for disconnectingthem, and means responslve to the engagement of all of the common trunksfor establishing at each zone office a busy condition indicating thatall of the common 10 trunks are engaged.

In Witness whereof, I hereunto subscribe my name this 27th day ofOctober A. D. 1925.

HERBERT B. JOHNSON.

